Apparatus and method of controlling linear compressor

ABSTRACT

A linear compressor control apparatus including a position detecting unit to detect the position of a piston and a compensation unit to compensate for output distortion of the position sensor. The compensation unit compensates for output distortion of the position sensor, caused by internal temperature of the linear compressor and load variation. Further, the compensation unit separates a high frequency signal and a DC signal from the output of the position detecting unit, and simultaneously performs position and temperature detecting operations using the separated high frequency signal and the DC signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Korean Application No.2002-11026, filed Feb. 28, 2002, and Application No. 2002-61895, filedOct. 10, 2002, in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to an apparatus andmethod of controlling a linear compressor, which compensates for outputdistortion of a position sensor for detecting the position of a piston.

[0004] 2. Description of the Related Art

[0005]FIG. 1 is a block diagram of a conventional apparatus to control alinear compressor.

[0006] Referring to FIG. 1, the conventional control apparatus iscomprised of a magnetic core 10, first and second coils 12 and 13, asignal processing unit 20 and a microcomputer 26. The magnetic core 10operates in conjunction with a mechanism whose position is to bedetected (not shown), the first and second coils 12 and 13 aresymmetrically wound around the core 10, and the signal processing unit20 detects and outputs variations in position of the core 10 usingvoltages induced to the first and second coils 12 and 13.

[0007] The signal processing unit 20 is comprised of a first full-waverectifying unit 21, a second full-wave rectifying unit 22, adifferential amplifying unit 23, a filter unit 24, and a peak detectingunit 25. The first full-wave rectifying unit 21 full-wave rectifiesvoltage induced to the first coil 12, the second full-wave rectifyingunit 22 full-wave rectifies voltage induced to the second coil 13, thedifferential amplifying unit 23 amplifies a difference between voltagesfull-wave rectified by the first and second full-wave rectifying units21 and 22, the filter unit 24 eliminates a high-frequency component froma signal outputted from the differential amplifying unit 23, and thepeak detecting unit 25 detects the maximum and minimum values of asignal outputted from the filter unit 24, and transmits the detectedvalues to a microcomputer 26.

[0008] The operation of the conventional linear compressor is describedbelow.

[0009] If the position of the core 10 is varied by a variation inposition of the mechanism whose position is to be detected withalternating current (AC) having a frequency of several KHz applied tothe first and second coils 12 and 13 from the outside, voltages inproportion to the variation in position of the core 10 are induced tothe first and second coils 12 and 13. The voltages induced to the firstand second coils 12 and 13 are full-wave rectified by the first andsecond full-wave rectifying units 21 and 22 and the full-wave rectifiedvoltages are inputted to input terminals of the differential amplifyingunit 23.

[0010] The differential amplifying unit 23 amplifies a differencebetween the voltages full-wave rectified by the first and secondfull-wave rectifying units 21 and 22, and outputs the amplifieddifference to the filter unit 24. The filter unit 24 eliminates ahigh-frequency component from the signal outputted from the differentialamplifying unit 23, and outputs the filtered signal to the peakdetecting unit 25. The peak detecting unit 25 detects a peak of thesignal outputted from the filter unit 24, that is, a maximum stroke, andoutputs the detected maximum stroke to the microcomputer 26. Themicrocomputer 26 controls the stroke of the linear compressor 1according to the maximum stroke.

[0011] In the conventional linear compressor control apparatus, theoutput control of the linear compressor is performed by controlling theposition of the piston on the basis of voltage values detected by thefirst and second coils 12 and 13. However, as resistances of the coilsare increased according to a temperature, the output value of the firstand second coils 12 and 13 is also increased. Further, the center of aresonance point of the piston is shifted according to the variation of aload. At this time, if the center of the resonance point of the pistonmoves away from the valve relative to an initial assembled position, theoutput value is decreased, while if the center thereof approaches thevalve, the output value is increased.

[0012] That is, the first and second coils 12 and 13 serve to detect theposition of the piston. In this case, the output value of the first andsecond coils 12 and 13 is varied according to an internal temperature ofthe compressor. Further, if the load is varied unstably, the center ofthe resonance point of the piston is shifted, so the output voltage maychange.

[0013] As described above, if the position of the piston is controlledusing the voltage values detected by conventional first and secondcoils, the center of the resonance point is shifted due to the internaltemperature of the compressor or the load variation, so the output valueof the coils at the same top clearance is distorted, thus preventing anoptimal top clearance from being maintained. In the worst case, abnormalphenomena, such as a collision of the piston of the compressor with thevalve, etc., may occur.

[0014] If the top clearance is set to be larger to avoid the collisionof the piston, the size of the compressor must be increased inproportion to the increased top clearance so as to obtain cooling power(output) of desired intensity, thereby causing a burden in manufacturinga compressor.

SUMMARY OF THE INVENTION

[0015] Accordingly, it is an aspect of the present invention to providean apparatus and method of controlling a linear compressor, which maycompensate for a sensor output distorted due to an internal temperatureof the compressor or a load variation.

[0016] Additional aspects and advantages of the invention will be setforth in part in the description which follows and, in part, will beobvious from the description, or may be learned by practice of theinvention.

[0017] The foregoing and/or other aspects of the present invention areachieved by providing an apparatus to control a linear compressor havinga piston reciprocating in a cylinder of the linear compressor,comprising: a position detecting unit to detect a position of a pistonreciprocating in a cylinder of the linear compressor; and a compensatingunit to compensate for output distortion of the position detecting unitdue to internal temperature of the compressor and load variation.

[0018] The foregoing and/or other aspects of the present invention arealso achieved by providing a method of controlling a linear compressorhaving a position detecting unit to detect a position of a piston of thelinear compressor, comprising: supplying alternating current (AC) powerto the position detecting unit, detecting the position of the pistonaccording to an output of the position detecting unit, and detecting aload according to the detected position of the piston; supplying directcurrent (DC) power to the position detecting unit and detecting internaltemperature of the linear compressor according to the output of theposition detecting unit; and compensating for output distortion of theposition detecting unit according to the detected internal temperatureof the linear compressor and the detected load.

[0019] The foregoing and/or other aspects of the present invention arealso achieved by providing a method of controlling a linear compressorhaving a position detecting unit to detect a position of a piston of thelinear compressor, comprising: detecting internal temperature of thelinear compressor; detecting the amount of shift of a resonance point ofthe piston; compensating for an error of a maximum stroke of the pistondetected by the position detecting unit according to the internaltemperature of the linear compressor and the amount of shift of thepiston resonance point; and driving the linear compressor according tothe compensated maximum stroke.

[0020] The foregoing and/or other aspects of the present invention arealso achieved by providing an apparatus to control a linear compressor,comprising a position detecting unit to detect a position of a pistonreciprocating in a cylinder of the linear compressor; a power supplyunit to supply drive power to the position detecting unit; and acompensating unit to compensate for output distortion of the positiondetecting unit due to internal temperature of the linear compressor.

[0021] The foregoing and/or other aspects of the present invention arealso achieved by providing an apparatus to control a linear compressor,comprising: a position detecting unit to detect a position of a pistonreciprocating in a cylinder of the linear compressor; a power supplyunit to supply drive power to the position detecting unit; and acompensating unit to calculate the amount of shift of a piston resonancepoint and a load from the position of the piston, and compensate foroutput distortion of the position detecting unit on the basis of thecalculated load.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other aspects and advantages of the invention willbecome apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

[0023]FIG. 1 is a block diagram of a conventional apparatus to control alinear compressor;

[0024]FIG. 2 is a block diagram of an apparatus to control a linearcompressor according to an embodiment of the present invention;

[0025]FIG. 3 is a circuit diagram to receive AC power for detecting theposition of a piston in the control apparatus of the linear compressorof FIG. 2;

[0026]FIG. 4 is a circuit diagram to receive DC power for detecting theinternal temperature of the compressor in the control apparatus of thelinear compressor of FIG. 2;

[0027]FIG. 5 is a circuit diagram of a resonance point shift detectingunit in the control apparatus of the linear compressor of FIG. 2;

[0028]FIG. 6 is a graph illustrating errors of a sensor output due to aninternal temperature of the linear compressor of FIG. 2;

[0029]FIG. 7 is a graph illustrating compensated strokes correspondingto the amount of shift of a resonance point according to conditions ofthe control apparatus of the linear compressor of FIG. 2;

[0030]FIG. 8 is a flowchart of a temperature detecting routine accordingto an embodiment of the present invention;

[0031]FIG. 9 is a flowchart of a position calculating routine accordingto an embodiment of the present invention;

[0032]FIG. 10 is a flowchart of a load amount calculating routineaccording to an embodiment of the present invention;

[0033]FIG. 11 is a block diagram of another apparatus to control alinear compressor according to another embodiment of the presentinvention; and

[0034]FIG. 12 is a block diagram of a further apparatus to control alinear compressor according to a modified embodiment of FIG. 11 toillustrate the operation of correcting position information according toinputted temperature information by an instruction value calculatingunit of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Reference will now be made in detail to the embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

[0036] A first embodiment is described with respect to a case whereoutput distortion of a position sensor is compensated by consideringboth an internal temperature of a compressor and a load, and a secondembodiment is described with respect to a case where output distortionof a position sensor is compensated by considering only an internaltemperature of the compressor.

[0037]FIG. 2 is a block diagram of an apparatus to control a linearcompressor according to an embodiment of the present invention. The samereference numerals as those of FIG. 1 are used in FIG. 2 to designatethe same or similar components.

[0038] Referring to FIG. 2, the linear compressor control apparatusincludes a magnetic core 10 to operate in conjunction with a mechanismwhose position is to be detected, and a position detecting unit havingfirst and second coils 12 and 13 symmetrically wound around the outerside of the core 10.

[0039] A position detecting unit 20 includes first and second rectifyingunits 21 and 22, a differential amplifying unit 23, a filter unit 24 anda peak detecting unit 25. The first rectifying unit 21 full-waverectifies a voltage induced to the first coil 12, and the secondrectifying unit 22 full-wave rectifies a voltage induced to the secondcoil 13. The differential amplifying unit 23 amplifies a differencebetween voltages full-wave rectified by the first and second rectifyingunits 21 and 22. The filter unit 24 eliminates a high-frequencycomponent from an output signal of the differential amplifying unit 23.The peak detecting unit 25 detects a maximum stroke from an outputsignal of the filter unit 24.

[0040] The position detecting unit further includes a power supply unit14 to supply a alternating current (AC) power or direct current (DC)power to one-side ends of the first and second coils 12 and 13 connectedin series.

[0041] The linear compressor control apparatus of the present inventioncomprises a compensating unit 30 to compensate for output distortion ofthe position detecting unit due to the internal temperature of thelinear compressor and load variation.

[0042] The compensating unit 30 comprises a temperature detecting unit31, a resonance point shift detecting unit 32, a position calculatingunit 33, a load amount calculating unit 34 and an instruction valuecalculating unit 35.

[0043] The power supply unit 14 serves to supply AC power to detect thepiston of the piston, or DC power to detect internal temperature of thecompressor. This power supply unit 14 supplies one of the AC power andthe DC power according to an output signal of the temperature detectingunit 31.

[0044] The temperature detecting unit 31 determines the variation of theload according to a shift change rate of a resonance point (Δ resonancepoint shift data) and provides an AC supply instruction to the powersupply unit 14 when the load is unstable, so the power supply unit 14supplies AC power, as illustrated in FIG. 3. On the other hand, when theload is stable, the temperature detecting unit 31 provides a DC supplyinstruction to the power supply unit 14, so the power supply unit 14supplies DC power, as illustrated in FIG. 4.

[0045] A case where the power supply unit 14 supplies AC power ismodeled as illustrated in a circuit diagram of FIG. 3. AC power Vac issupplied to one-side ends of the first and second coils 12 and 13connected in series. Inductance L1 of the first coil 12 and inductanceL2 of the second coil 13 vary according to the variation of the positionof the core 10, which operates in conjunction with the piston.Therefore, a voltage proportional to the variations of the inductancesL1 and L2 is outputted through resistors R1 and R2, a rectifying diodeD1 and a capacitor C. The output voltage is induced to the first andsecond coils 12 and 13, respectively. The induced voltages are providedto the first and second rectifying units 21 and 22 and the temperaturedetecting unit 31 as information used to detect the position of thepiston.

[0046] A case where the power supply unit 14 supplies DC power ismodeled as illustrated in a circuit diagram of FIG. 4. In this case, DCpower Vdc is supplied to one-side ends of the first and second coils 12and 13 connected in series. Inductance L1 of the first coil 12 andinductance L2 of the second coil 13 vary according to the temperature ofthe linear compressor (internal temperature of the linear compressor).Therefore, a voltage proportional to the variations of the inductancesL1 and L2 is outputted through the resistors R1 and R2, the rectifyingdiode D1 and the capacitor C. The output voltage is induced to the firstand second coils 12 and 13, respectively. The induced voltages areprovided to the first and second rectifying units 21 and 22 and thetemperature detecting unit 31 as information used to detect thetemperature of the linear compressor.

[0047] The temperature detecting unit 31 converts a temperaturedetecting signal corresponding to the induced voltages into digitaltemperature data, and outputs the temperature data to the positioncalculating unit 33.

[0048] If the power supply unit 14 supplies AC power, voltagesproportional to variation of the position of the core 10 are induced tothe first and second coils 12 and 13. The induced voltages are full-waverectified by the first and second rectifying units 21 and 22, and theninputted to input terminals of the differential amplifying unit 23. Thedifferential amplifying unit 23 amplifies a difference between theinputted voltages and outputs the amplified result to the filter unit24. The filter unit 24 eliminates a high-frequency component from theamplified output signal and outputs the eliminated result to both theresonance point shift detecting unit 32 and the peak detecting unit 25.The peak detecting unit 25 detects a maximum stroke of the piston andoutputs the detected result as maximum stroke data to the positioncalculating unit 33.

[0049]FIG. 5 is a circuit diagram of the resonance point shift detectingunit 32 according to an embodiment of the present invention. Theresonance point shift detecting unit 32 comprises an operationalamplifier OP, resistors Ra, Rb and Rc, and a capacitor Ca.

[0050] The resonance point shift detecting unit 32 detects resonancepoint shift data indicating a shifting state of the center of theresonance point from the signal provided by the filter unit 24, andoutputs the resonance point shift data to the position calculating unit33 and the load amount calculating unit 34.

[0051] As illustrated in FIG. 6, as an internal temperature of thecompressor becomes high, a compensated sensor output S1, that is, eachof voltages induced to the first and second coils 12 and 13, becomeslarger than a sensor output S2 which is not compensated. Therefore, asthe internal temperature of the compressor becomes high, an error of thesensor output becomes larger, thus requiring a method of coping withsuch an error.

[0052] As illustrated in FIG. 7, the compensated strokes correspondingto the amount of shift of the resonance point increase. In this case,differences between suction pressure and discharge pressure of thecompressor satisfy the relation G1>G2>G3>G4.

[0053] The position calculating unit 33 compensates for an error of thetop clearance using the maximum stroke data obtained by converting themaximum stroke calculated on the basis of maximum values and minimumvalues of the output signal of the filter unit 24 into digital data, thetemperature data obtained by converting the temperature detecting signaloutputted from the temperature detecting unit 31 into digital data, andthe resonance point shift data obtained by converting the resonancepoint shift signal outputted from the resonance point shift detectingunit 32 into digital data. Further, the position calculating unit 33outputs compensated top clearance information to the instruction valuecalculating unit 35.

[0054] The load amount calculating unit 34 outputs an instruction valuedetermined according to the resonance point shift data outputted fromthe resonance point shift detecting unit 32 and a preset value to theinstruction value calculating unit 35.

[0055] The instruction value calculating unit 35 outputs a drive signalto drive the linear compressor 37 to the compressor driving unit 36according to the top clearance outputted from the position calculatingunit 33 and the instruction value outputted from the load amountcalculating unit 34.

[0056] The compressor driving unit 36 drives the linear compressor 37according to the drive signal outputted from the instruction valuecalculating unit 35.

[0057] A control method of the linear compressor control apparatushaving the above construction according to an embodiment of the presentinvention is herein described below in detail.

[0058]FIG. 8 illustrates a temperature detecting routine performed bythe temperature detecting unit 31. First, when the power supply unit 14supplies AC power, the temperature detecting unit 31 calculates a shiftchange rate of the resonance point (Δ resonance point shift data) fromthe signal outputted from the circuit of FIG. 3 at operation S10. Inthis case, the resonance point shift change rate is calculated by thefollowing equation.

Δ resonance point shift data=previous resonance point shift data−currentresonance point shift data

[0059] The temperature detecting unit 31 determines whether anactivating time of the linear compressor, which is counted using a firstcounter (not shown), exceeds a preset time A at operation S11. If thecompressor activating time exceeds the preset time A, the temperaturedetecting unit 31 determines whether the resonance point shift changerate (Δ resonance point shift data) is less than a preset change rate Bat operation S12. A time after the time point of the determination iscounted using a second counter (not shown).

[0060] If the resonance point shift change rate is less than the presetchange rate B according to the determined result at operation S12, thetemperature detecting unit 31 determines whether the counted time by thesecond counter reaches a preset time D at operation S13. If the countedtime by the second counter reaches the preset time D, the temperaturedetecting unit 31 outputs a dc signal DC to the power supply unit 14 toallow the power supply unit 14 to supply DC power. In this way, as theDC power is supplied, the temperature detecting unit 31 performs anoperation of providing temperature data obtained by converting a signalproportional to the voltages induced to the first and second coils 12and 13 into digital data to the position calculating unit 33, that is, atemperature sensing operation at operation S14.

[0061] If the compressor activating time does not exceed the preset timeA at operation S11, if the resonance point shift change rate (Δresonance point shift data) is not less than the preset change rate B atoperation S12, and if the counted time does not reach the preset time Dat operation S13, the temperature detecting unit 31 outputs an ac signalAC to the power supply unit 14 to allow the power supply unit 14 tosupply AC power.

[0062]FIG. 9 illustrates a position calculating routine performed by theposition calculating unit 33. First, the position calculating unit 33receives the temperature data from the temperature detecting unit 31,the resonance point shift data from the resonance point shift detectingunit 32, and piston position information, which is outputted from thepeak detecting unit 25 when the power supply unit 14 supplies AC power,that is, maximum stroke data at operation S20.

[0063] The position calculating unit 33 searches a lookup table for amaximum stroke corresponding to the temperature data and the resonancepoint shift data at operation S21. Then, the position calculating unit33 outputs the searched maximum stroke, that is, a maximum strokecompensated according to the internal temperature of the compressor andthe amount of shift of the resonance point, to the instruction valuecalculating unit 35 at operation S22. This means that an error of thesensor output due to the internal temperature of the compressor and theamount of shift of the resonance point is corrected when the linearcompressor is driven with the compensated maximum stroke. Consequently,the error correction of the sensor output results in the compensation ofan error of the top clearance.

[0064] The linear compressor has excellent characteristics in varianceof its capacity compared with conventional AC motors. Therefore, thecapacity of the linear compressor may be varied appropriately accordingto load information calculated by the load amount calculating unit 34.

[0065]FIG. 10 illustrates a load amount calculating routine performed bythe load amount calculating unit 34. First, the load amount calculatingunit 34 determines whether the activating time of the compressor exceedsa preset time C at operation S30. If the compressor activating timeexceeds the preset time C, the load amount calculating unit 34 comparesresonance point shift information, that is, the resonance point shiftdata received from the resonance point shift detecting unit 32, with apreset value, determines an instruction value corresponding to a loadstate, and outputs the determined instruction value to the instructionvalue calculating unit 35 at operation S31. If the compressor activatingtime does not exceed the preset time C, the load amount calculating unit34 determines an instruction value for a normal load condition in aninitial operation of the compressor and outputs the instruction value tothe instruction value calculating unit 35 at operation S32.

[0066] As described above, the instruction value calculating unit 35outputs a drive instruction to drive the linear compressor to thecompressor driving unit 36 using the instruction value determinedaccording to the maximum stroke compensated by the position calculatingunit 33 and the load information calculated by the load amountcalculating unit 34.

[0067] The previous embodiment compensates for output distortion of theposition sensor by considering an internal temperature of the compressorand the amount of a load, wherein the power supply unit must alternatelysupply AC power and DC power according to the condition of a load.

[0068] However, if a power supply period is short (for example, 120 Hz),a compensation process considering both of a temperature and a load iscomplicated. Accordingly, in the following embodiment as describedbelow, drive power obtained by overlapping a DC voltage and a highfrequency signal is supplied to the position sensor so as tosimultaneously perform an operation of detecting the position of apiston and an operation of detecting the internal temperature of thecompressor, a high frequency signal and a DC signal are separated fromthe signal outputted from the position sensor, the separated highfrequency signal being used as a position detection signal, and theseparated DC signal is used as a temperature detection signal, thusenabling position information and temperature info information to besimultaneously obtained.

[0069]FIG. 11 is a block diagram of an apparatus to control a linearcompressor according to another embodiment of the present invention. Thelinear compressor control apparatus of this embodiment uses a manner ofoverlapping a signal used to obtain position detection (signal with afrequency higher than several KHz) and a signal used to obtaintemperature detection (certain DC voltage).

[0070] As illustrated in FIG. 11, the linear compressor controlapparatus of this embodiment includes a high frequency signal generatingunit 61, a DC voltage generating unit 63 and an adder 65 which supplypower to a position sensor 67.

[0071] The position sensor 67 includes a magnetic core, and first andsecond coils symmetrically wound around the outer side of the magneticcore. The position sensor 67 is connected to resistors R1 and R2, and isconnected to the adder 65 through the resistor R1.

[0072] The high frequency signal generating unit 61 supplies a highfrequency signal (several KHz) to the adder 65, and the DC voltagegenerating unit 63 supplies a certain DC voltage to the adder 65. Theadder 65 overlaps the certain DC voltage and the high frequency signal,and supplies the overlapped voltage to the position sensor 67.

[0073] One output from the position sensor 67 is inputted to adifferential amplifier 69 through a rectifier 68. The differentialamplifier 69 compares a sensor output signal rectified by the rectifier68 and a preset reference signal. On the basis of the comparison result,a difference between the two input signals is calculated and adifference signal is outputted to a low pass filter 71. A signaloutputted from the low pass filter 71 is used as position information.Such position information is a signal (for example, 60 Hz) used todetect the position of the piston, which is provided to a positioncalculating unit 79 through a peak detecting unit 73.

[0074] The other output from the position sensor 67, having acharacteristic that its value is decreased if a surrounding temperatureis increased, is provided to a temperature detecting low pass filter 75.In this case, a high frequency signal of the output value is variedaccording to the position of the piston. Therefore, a low pass filterhaving a cut-off frequency of several Hz is used as the low pass filter75. The low pass filter 75 separates only a DC signal from the inputtedsignal. The separated DC signal is amplified to an appropriate level byan amplifier 77 for the purpose of signal processing. The amplifiedsignal is provided to the position calculating unit 79 as temperatureinformation.

[0075] The position calculating unit 79 corrects the positioninformation on the basis of the temperature information, and providesthe temperature-corrected position information to an instruction valuecalculating unit 81. The instruction value calculating unit 81 convertsthe temperature-corrected position information into digital information,and outputs a control signal to a compressor driving unit 83 to drivethe compressor on the basis of the digital position information.Accordingly, the compressor driving unit 83 outputs a drive signal tothe compressor to drive the compressor.

[0076] However, as a temperature increases, the value of the positioninformation increases, while the value of the temperature informationdecreases. The temperature information and the position information musthave a linear relationship in order for the position calculating unit 79to employ a manner in which the position information is added to theamplified temperature information to correct the position information.

[0077] Therefore, a modified embodiment shown in FIG. 12 is applied tothe present invention to provide against a case where the temperatureinformation and the position information do not have a linearrelationship.

[0078]FIG. 12 is a block diagram of another embodiment of an apparatusto control a linear compressor according to a modified embodiment ofFIG. 11 to illustrate the operation of correcting position informationaccording to inputted temperature information by an instruction valuecalculating unit of FIG. 11.

[0079] Referring to FIG. 12, the linear compressor control apparatusemploys a method in which a signal used to obtain position detection(several KHz), generated by the high frequency signal generating unit61, and a signal used to obtain temperature detection (certain DCvoltage), generated by the DC voltage generating unit 63, are overlappedby the adder 65, and the overlapped signal is provided to the positionsensor 67. One output from the position sensor 67 passes through therectifier 68, the differential amplifier 69, the low pass filter 71 andthe peak detecting unit 73, and is provided to an instruction valuecalculating unit 81 a as position information. The other output from theposition sensor 67 passes through the low pass filter 75, and isprovided to the instruction value calculating unit 81 a as temperatureinformation.

[0080] The instruction value calculating unit 81 a converts the positioninformation and the temperature information into digital information,respectively, and corrects the position information according to thedigital temperature information. In this case, the instruction valuecalculating unit 81 a uses a preset lookup table to correct the positioninformation by the temperature information and the position informationwhich have a non-linear relationship. Temperature-corrected positioninformation is provided to the compressor driving unit 83. Thecompressor driving unit outputs a drive signal to the compressor todrive the compressor.

[0081] Even though not described in the above embodiment, it is possibleto compensate for output distortion of the position sensor byconsidering only a load variation, which may be easily appreciated bythose skilled in the field from the embodiment of FIG. 2.

[0082] As described above, the present invention provides an apparatusand method of controlling a linear compressor, which compensates fordistortion of a sensor output caused by the shifting of the center of aresonance point due to internal temperature of the compressor and loadvariation in driving the linear compressor according to the position ofa piston, thus enabling the linear compressor to be controlled with anoptimal top clearance and consequently improving control accuracy.Further, the present invention varies the capacity of the compressorappropriately on the basis of load information obtained according toresonance point shift data, thereby enabling the linear compressor toactively cope with load variation by itself, and consequently reducingpower consumption.

[0083] Further, the present invention is advantageous in that a highfrequency signal and a DC voltage are overlapped to be provided to aposition sensor, a high frequency signal and a DC signal are separatedfrom an output of the position sensor, and the separated high frequencysignal and the DC signal are used as a position detection signal and atemperature detection signal, respectively, thus enabling positiondetection and temperature detection to be simultaneously performed, andeasily implementing hardware for position and temperature detection.

[0084] Although a few embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made to the above embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined in the claims and their equivalents.

What is claimed is:
 1. An apparatus to control a linear compressorhaving a piston reciprocating in a cylinder of the linear compressor,comprising: a position detecting unit to detect a position of a pistonreciprocating in a cylinder of the linear compressor; and a compensatingunit to compensate for output distortion of the position detecting unitdue to internal temperature of the compressor and load variation.
 2. Thelinear compressor control apparatus according to claim 1, wherein saidposition detecting unit detects the position of the piston whenalternating current (AC) power is supplied and detects the internaltemperature of the compressor when direct current (DC) power issupplied.
 3. The linear compressor control apparatus according to claim2, further comprising a power supply unit to selectively supply AC powerand DC power to the position detecting unit.
 4. The linear compressorcontrol apparatus according to claim 3, wherein said power supply unitsupplies the AC power to the position sensor if the load is unstable andsupplies the DC power to the position sensor if the load is stable. 5.The linear compressor control apparatus according to claim 1, whereinsaid compensation unit comprises: a temperature detecting unit to detectthe internal temperature of the linear compressor; a resonance pointshift detecting unit to detect the amount of shift of a piston resonancepoint due to the load variation; a position calculating unit tocompensate for an error of a maximum stroke of the piston detected bythe position detecting unit according to the internal temperature of thelinear compressor and the amount of shift of the piston resonance point;and an instruction value calculating unit to output a drive instructionto drive the linear compressor according to the maximum strokecompensated by the position calculating unit.
 6. The linear compressorcontrol apparatus according to claim 5, wherein said compensating unitfurther comprises a load amount calculating unit to calculate the amountof load according to the amount of shift of the piston resonance pointand the instruction value calculating unit drives the linear compressorby considering the calculated load amount.
 7. A method of controlling alinear compressor having a position detecting unit to detect a positionof a piston of the linear compressor, comprising: supplying alternatingcurrent (AC) power to the position detecting unit, detecting theposition of the piston according to an output of the position detectingunit, and detecting a load according to the detected position of thepiston; supplying direct current (DC) power to the position detectingunit and detecting internal temperature of the linear compressoraccording to the output of the position detecting unit; and compensatingfor output distortion of the position detecting unit according to thedetected internal temperature of the linear compressor and the detectedload.
 8. The linear compressor control method according to claim 7,wherein said internal temperature of the linear compressor is detectedwhen an activating time of the compressor is counted and a countedactivating time exceeds a preset time.
 9. A method of controlling alinear compressor having a position detecting unit to detect a positionof a piston of the linear compressor, comprising: detecting internaltemperature of the linear compressor; detecting the amount of shift of aresonance point of the piston; compensating for an error of a maximumstroke of the piston detected by the position detecting unit accordingto the internal temperature of the linear compressor and the amount ofshift of the piston resonance point; and driving the linear compressoraccording to the compensated maximum stroke.
 10. An apparatus to controla linear compressor, comprising: a position detecting unit to detect aposition of a piston reciprocating in a cylinder of the linearcompressor; a power supply unit to supply drive power to the positiondetecting unit; and a compensating unit to compensate for outputdistortion of the position detecting unit due to internal temperature ofthe linear compressor.
 11. The linear compressor control apparatusaccording to claim 10, wherein said power supply unit supplies drivepower obtained by overlapping a high frequency signal for detecting theposition of the piston and a direct current (DC) voltage for detectingthe internal temperature of the linear compressor.
 12. The linearcompressor control apparatus according to claim 11, wherein said powersupply unit comprises: a high frequency signal generating unit togenerate the high frequency signal; a DC voltage generating unit togenerate the DC voltage with a predetermined level; and an adder tooverlap the DC voltage and the high frequency signal.
 13. The linearcompressor control apparatus according to claim 10, wherein saidcompensation unit comprises a low pass filter to eliminate a highfrequency component from an output of the position detecting unit, andcompensates for output distortion of the position detecting unit using asignal whose high frequency component is eliminated by the low passfilter.
 14. The linear compressor control apparatus according to claim13, wherein said compensation unit comprises: a position calculatingunit to amplify the internal temperature information and then correctingposition information, if the temperature information whose highfrequency component is eliminated by the low pass filter and theposition information obtained from the output of the position detectingunit have a linear relationship; and an instruction value calculatingunit to output a drive signal to drive the linear compressor on thebasis of the position information which is corrected by the positioncalculating unit.
 15. The linear compressor control apparatus accordingto claim 13, wherein said compensation unit further comprises: aninstruction value calculating unit to receive temperature informationand position information, respectively, correct the position informationaccording to the temperature information using a preset lookup table,and output a drive signal to drive the compressor on the basis of thecorrected position information, if the temperature information whosehigh frequency component is eliminated by the low pass filter and theposition information obtained from the output of the position sensorhave a non-linear relationship.
 16. An apparatus to control a linearcompressor, comprising: a position detecting unit to detect a positionof a piston reciprocating in a cylinder of the linear compressor; apower supply unit to supply drive power to the position detecting unit;and a compensating unit to calculate the amount of shift of a pistonresonance point and a load from the position of the piston, andcompensate for output distortion of the position detecting unit on thebasis of the calculated load.
 17. The linear compressor controlapparatus according to claim 16, wherein said power supply unit suppliesalternating current (AC) power to the position detecting unit.
 18. Thelinear compressor control apparatus according to claim 5, wherein thetemperature detecting unit determines the variation of the loadaccording to a shift change rate of a resonance point (Δ resonance pointshift data) and provides an AC supply instruction to the power supplyunit 14 when the load is unstable so the power supply unit 14 suppliesAC power, or the temperature detecting unit 31 provides a DC supplyinstruction to the power supply unit 14 when the load is stable so thepower supply unit 14 supplies DC power.
 19. An apparatus to control alinear compressor comprising: a high frequency signal generating unit; aDC voltage generating unit; an adder to add the outputs of both the highfrequency signal generating unit and the DC voltage generating unit; anda position sensor to receive the output from the adder a provide twosensor output signals.
 20. The linear compressor control apparatusaccording to claim 19, wherein the position sensor comprises: a magneticcore; and first and second coils symmetrically would around the magneticcore.
 21. The linear compressor control apparatus according to claim 19,wherein the position sensor is connected at one end to the a highfrequency signal generating unit through a first resistor and at anotherend to a potential through a second resistor.
 22. The linear compressorcontrol apparatus according to claim 21, wherein the adder overlaps DCvoltage and the high frequency signal and supplies the overlappedvoltage to the position sensor.
 23. The linear compressor controlapparatus according to claim 22, further comprising: a rectifier torectify one of the sensor output signals; a differential amplifier toreceive the rectified sensor output signal from the position sensor andcompare the rectified signal with a preset reference signal to provide adifference signal; a low pass filter to receive the difference signaland provide position information; a peak detecting unit to receive theposition information and output the position information; and a positioncalculating unit to receive the position information from the peakdetecting unit.
 24. The linear compressor control apparatus according toclaim 23, further comprising: a low pass filter to receive the secondsensor output signal having a characteristic that a value thereof isdecreased if a surrounding temperature is increased, wherein a highfrequency signal of the second sensor output signal is varied accordingto the position of the piston.
 25. The linear compressor controlapparatus according to claim 24, wherein the low pass filter has acutoff of several Hertz and separates only a DC signal.
 26. The linearcompressor control apparatus according to claim 24, further comprising:an amplifier to amplify the separated DC signal and provide theamplified signal to the position calculating unit as temperatureinformation.
 27. The linear compressor control apparatus according toclaim 26, wherein the position calculation unit corrects the positioninformation on the basis of the temperature information.
 28. The linearcompressor control apparatus according to claim 27, further comprising:an instruction value calculating unit to receive thetemperature-corrected position information and convert thetemperature-corrected position information into digital information; anda compressor driving unit driving the linear compressor based on thedigital information output received from the instruction valuecalculating unit.
 29. The linear compressor control apparatus accordingto claim 22, further comprising: a rectifier to rectify one of thesensor output signals; a differential amplifier to receive the rectifiedsensor output signal from the rectifier and compare the rectified sensoroutput signal with a preset reference signal to provide a differencesignal; a low pass filter to receive the difference signal and provideposition information; and a peak detecting unit to receive the positioninformation and output the position information.
 30. The linearcompressor control apparatus according to claim 29, further comprising:a low pass filter to output temperature information from determined fromthe second sensor output signal received from the position sensor, thetemperature information output having a characteristic that a valuethereof is decreased if a surrounding temperature is increased, whereina high frequency signal of the second sensor output signal is variedaccording to the position of the piston.
 31. The linear compressorcontrol apparatus according to claim 30, further comprising: aninstruction value calculating unit to receive the position informationfrom the peak detecting unit and the temperature information output fromthe low pass filter and converts the position information andtemperature information signals into digital information, and correctsthe position information according to the digital temperatureinformation; and a compressor driving unit to drive the linearcompressor according to the information received from the instructionvalue calculating unit.
 32. The linear compressor control apparatusaccording to claim 31, wherein the instruction value calculating unituses a lookup table to correct the position information by thetemperature information and the position information.
 33. A linearcompressor control apparatus comprising: a high frequency signalgenerating unit to generate a high frequency signal; a DC voltagegenerating unit to generate a DC voltage; an adder to overlap the highfrequency signal and the DC voltage signal; and a position sensor toreceive the output from the adder and separate a high frequency signaland a DC signal to be used as a position detection signal and atemperature detection signal, respectively, such that position detectionand temperature detection are performed simultaneously.